/Engine/Plugins/Experimental/PCG/Source/PCG/Public/Elements/Metadata/PCGMetadataOpElementBase.h
All operations can have a fixed number of inputs and a variable number of outputs. Each output need to have its own callback, all taking the exact number of "const InType&" as input and each can return a different output type.
template<typename InType, typename... Callbacks> bool DoUnaryOp ( [FOperationData](API\Plugins\PCG\Elements\Metadata\FPCGMetadataElementBase\FOperationData) & InOperationData, Callbacks &&... InCallbacks ) const